766346 - CSS 3D visual errors with software webrender

Status: REOPENED

(Core :: Graphics: WebRender, defect)

Description

[Bobby Richter [:secretrobotron]]

http://k88hudson.github.com/sadcube/

The link above will lead to a page with a simple (yet sad) spinning cube. With layers acceleration enabled, the cube appears as expected. Without layers acceleration, however, the cube's constituent planes and its shadow shake violently.

Comment 1

[Benoit Jacob [:bjacob] (mostly away)]

This is confirmed on both Mac and Linux.

Comment 2

[Joe Drew (not getting mail)]

We implement 3D transforms using pixman when we don't have hardware acceleration. Sounds like there's something wrong with that implementation.

Comment 3

[Benoit Jacob [:bjacob] (mostly away)]

The "shaking" we're seeing here seems too much to be explained by pixman bugs. The cube seems to be making "two steps forward, one step back" kind of dance.

Comment 4

[Benoit Jacob [:bjacob] (mostly away)]

Though: does pixman do matrix transforms? If yes, the bug could be explained by a bug there.

Comment 5

[Matt Woodrow (:mattwoodrow)]

Attachment: Use skia for BasicLayers 3d transforms

This is definitely a pixman issue.

Attached is a patch that switches the rendering of BasicLayers 3d-transforms to be done via skia instead.

This fixes the wobbling for me. Quality still is pretty low (unsurprisingly).

Comment 6

[Jeff Muizelaar [:jrmuizel]]

(In reply to Matt Woodrow (:mattwoodrow) from comment #5)
> Created attachment 634678 [details] [diff] [review]
> Use skia for BasicLayers 3d transforms
> 
> This is definitely a pixman issue.
> 
> Attached is a patch that switches the rendering of BasicLayers 3d-transforms
> to be done via skia instead.
> 
> This fixes the wobbling for me. Quality still is pretty low (unsurprisingly).

It would be good to fix pixman too...

Comment 7

[Matt Woodrow (:mattwoodrow)]

(In reply to Jeff Muizelaar [:jrmuizel] from comment #6)
> It would be good to fix pixman too...

It looked to me like it was the result of rounding inaccuracies, not sure if that will be easy to fix.

That said, I don't disagree with your statement at all.

I think we should take my patch for the time being, without blocking this on finding someone to debug pixman.

Comment 8

[Virtual_ManPL [:Virtual] 🇵🇱 - (please needinfo? me - so I will see your comment/message/reply/question/etc.)]

So what's the final decision here?

Comment 9

[Jeff Muizelaar [:jrmuizel]]

Comment on attachment 634678 [details] [diff] [review]
Use skia for BasicLayers 3d transforms

Review of attachment 634678 [details] [diff] [review]:
-----------------------------------------------------------------

I'd like an explanation for why this is broken in pixman before taking the patch.

Comment 10

[Gregory Pappas [:gregp]]

Unable to reproduce in current versions.

Comment 11

[Gregory Pappas [:gregp]]

Oops actually this is still a problem with Software WebRender

Comment 12

[Gregory Pappas [:gregp]]

Attachment: flashing_artifacts_software_webrender.webm